Abstract:An approach for generating optical frequency comb (OFC) with tunable free spectral range (FSR) is proposed. Two Mach-Zehnder modulators (MZMs) driven by phase-shifted sinusoidal signals are cascaded to generate OFC with plentiful comb lines and the FSR controlled by the drive frequency. Subsequently, a linearly chirped fiber Bragg grating (LCFBG) and a phase modulator (PM) are used to increase the comb FSR by a particular integer multiple. Therefore, by simultaneously controlling the drive frequency of MZMs, the dispersion amount of the LCFBG and the drive signal of the PM, an OFC with desired FSR can be achieved.

Abstract:A visual reconstruction method was proposed based on fiber Bragg grating (FBG) sensors and an intelligent algorithm, aiming to solve the problems of low accuracy and complex reconstruction process in conventional reconstruction methods of flexible structures. Firstly, the wavelength data containing structural strain information was captured by FBG sensors, together with deformation displacement information. Subsequently, a predicted model was built based on an extreme learning machine (ELM) and further optimized by the particle swarm optimization (PSO) algorithm. Different deformation patterns were tested on an aluminum alloy plate, indicating the ability of the predicted model to produce the deformation displacement for reconstruction. The experimental results show that the maximum error can be as low as 0.050 mm, which verifies that the proposed method is feasible and satisfied with the deformation monitoring of the spacecraft structure.

Abstract:To improve the integration of Fano devices, we design a T-shaped waveguide coupling micro-ring resonator (MRR) structure to achieve a single cavity with Fano resonance in the whole spectral bands. The mathematical relationship between the phase factor, the coupling coefficient of the bus waveguide, and the Fano resonance slope extinction ratio (ER) is established. The electron beam exposure process is used to obtain a device with an insertion loss of ~3 dB. The maximum ER of the Fano lineshape exceeds 15 dB, and the slope ratio (SR) is 251.3 dB/nm. This design improves the compactness of the Fano resonant device.

Abstract:A novel dual-beam terahertz (THz) leaky-wave antenna (LWA) based on triple-periodically (TP) modulated spoof surface plasmon (SSP) waveguide is proposed. It is shown that SSP can be effectively excited and propagated along the surface of parallel corrugated metallic strips. Through proper design, the n=−1 and n=−2 Floquet modes are brought into the leakage radiation region simultaneously. Consequently, the forward and backward propagating waves corresponding to the two modes respectively generate two radiation beams in the far-field region. The proposed antenna is capable of steering the forward beam within a range of 34° and the backward beam within a range of 48° when frequency is swept between 0.23 THz and 0.29 THz. A simulated peak gain of 11.4 dBi and gain variation of 2.87 dBi are achieved within the band. The proposed LWA can be applied in THz wireless communication and radar systems.

Abstract:This study presents a simple methodology for implementation of all optical JK flip flop for future optical high speed networks. The scheme utilizes electronic model of JK flip flop for implementation of all optical JK flip flop at the bit rate of 7 Gbit/s. Firstly, all-optical AND and NOR gates are implemented. Furthermore, with the combination of these basic gate structures, the optical model of JK flip flop is verified. This structure makes use of two optical AND gates and two optical NOR gates. This technique uses a semiconductor optical amplifier (SOA) as the nonlinear medium to produce considerable amount of cross gain and cross phase modulation to attain truth table conditions of optical JK flip flop. In this method, the number of gates is reduced as compared to earlier schemes. Rise time and fall time of 5.6 ps with contrast ratio more than 60 dB are achieved in this design.

Abstract:In this work, we presented the measurements and calculations for the optimal pump conditions and their effects on thermal lens, fracture limit and laser efficiencies of end pumped Tm-doped yttrium aluminum perovskite (Tm:YAP) laser rod pumped at 1 064 nm. The results showed that the measured overall efficiency of produced laser at ~1.98 µm is enhanced from 3.9% to 6.9% when the pump spot diameter is reduced from 390 µm to 210 µm. The maximum output power and oscillation threshold are also enhanced with reduced pump spot size. The maximum thermal stress and focal length of thermally induced lens are also addressed.

Abstract:A novel dynamic photoresponse model for complementary metal-oxide-semiconductor (CMOS) image sensors with pinned photodiode (PPD) structures is proposed. The PPD is regarded as the bonding structure of the two p-n junctions. The transient current equation of the two junctions is calculated by the current-voltage formula of the p-n junction, and the photoresponse curve of the PPD is calculated and drawn by the numerical solution. Simulation results show that the dynamic model successfully restores the entire process of the electron accumulation in the PPD. The difference between the full well capacity (FWC) values which were calculated by the proposed model and the simulation results is less than 5%, which is much smaller than the error of 40% for the traditional model.

Abstract:In this paper, a localized surface plasmon resonance (LSPR) refractive index sensor based on photonic crystal fiber (PCF) is proposed to solve the problem of low refractive index analyte detection. 31 silver nanowires are placed on the surface of the D-shaped PCF, which increases the contact area between the plasma material and the analyte. The simulation results indicate that the maximum sensitivity of the sensor reaches 16 400 nm/RIU, and the refractive index detection range is 1.26—1.33. It is proved that the sensor has a good prospect in low refractive index detection.

Abstract:In this letter, single-walled carbon nanotubes (SWCNT) coating was used on the D-shaped silica fiber for ethanol sensing in aqueous solution. The performance of this structure as an ethanol sensor was studied here by monitoring output power variation and wavelength shift with changing ethanol concentration. In the concentration range of 5%—50% of ethanol, the SWCNT coated structure showed an improved sensitivity compared to the uncoated sample. The sensitivity is improved from 0.013 5 dB/% to 0.040 9 dB/% with the coating. The SWCNT coated sample also showed a peak wavelength shift of 0.1 nm with the change of ethanol concentration in the same range.

Abstract:Railway departments in various countries are looking for a technology with convenient operation, low price, excellent measurement performance and stability for spatial position measurement of railway track. Therefore, we design an optic-electronics stereo system based on the principle of optical stereo measurement. The experimental verification in the real railway environment shows that the performance of the system is that the longitudinal relative displacement measurement range is 200—10 000 mm, the relative distance measurement range is 4 500 mm and the measured root mean square (RMS) error value is less than 1.1 mm in the whole process. Therefore, it meets the relevant needs of the Russian Ministry of railways.

Abstract:As an ultra-precise instrument to characterize nano-morphology and structure, the morphology of atomic force microscopy (AFM) tip directly affects the quality of the scanned images, which in turn affects the measurement accuracy. In order to accurately characterize three-dimensional information of AFM tip, a reconstruction method of AFM tip using 2 μm lattice sample is researched. Under normal circumstances, an array of micro-nano structures is used to reconstruct the morphology of AFM tip. Therefore, the 2 μm lattice sample was developed based on semiconductor technology as a characterization tool for tip reconstruction. The experimental results show that the 2 μm lattice sample has good uniformity and consistency, and can be applied to the tip reconstruction method. In addition, the reconstruction method can accurately obtain the morphology of AFM tip, effectively eliminate the influence of the "probe effect" on the measurement results, and improve measurement accuracy.

Abstract:With the advantages of simple structure and fast training speed, broad learning system (BLS) has attracted attention in hyperspectral images (HSIs). However, BLS cannot make good use of the discriminative information contained in HSI, which limits the classification performance of BLS. In this paper, we propose a robust discriminative broad learning system (RDBLS). For the HSI classification, RDBLS introduces the total scatter matrix to construct a new loss function to participate in the training of BLS, and at the same time minimizes the feature distance within a class and maximizes the feature distance between classes, so as to improve the discriminative ability of BLS features. RDBLS inherits the advantages of the BLS, and to a certain extent, it solves the problem of insufficient learning in the limited HSI samples. The classification results of RDBLS are verified on three HSI datasets and are superior to other comparison methods.